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| United States Patent |
5,234,597
|
|
Welmers
, et al.
|
August 10, 1993
|
Solvent extraction process involving membrane separation of extract
phase and/or intermediate zone phase with pseudo extract/pseudo
raffinate recycle, preferably employing interfacially polymerized
membranes
Abstract
The solvent extraction of aromatics containing oil using a selective
aromatics extraction solvent to produce an aromatics rich extract phase
and an oil rich/aromatics lean raffinate is improved by the steps of
subjecting the extract phase to a membrane separation step to produce a
permeate phase and a retentate phase passing the retentate phase to a
settling zone wherein the retentate phase spontaneously separates into two
liquid phases, and recycling the upper phase to the extraction zone,
either to the feed inlet or to the bottom of the extract reflux zone to
thereby increase the raffinate oil recovered from the extraction tower.
Alternatively or in addition to the above, a side stream can be taken from
an intermediate zone of the extraction zone (e.g. extraction tower) and
fed to a membrane separation to produce a solvent rich permeate and an oil
rich retentate. The solvent rich permeate is recycled while the oil rich
retentate is fed to a settling zone wherein it will spontaneously separate
into an oil rich pseudo raffinate upper phase which is recovered and into
a solvent rich pseudo extract bottoms phase which is recycled to the
solvent extraction zone, preferably at a point below that at which the
side stream was withdrawn. The membrane separation zone preferably employs
interfacially polymerized membranes under reverse osmosis conditions.
| Inventors:
|
Welmers; Adrianus (Sarnia, CA);
Black; Laura E. (Sarnia, CA)
|
| Assignee:
|
Exxon Research & Engineering Company (Florham Park, NJ)
|
| Appl. No.:
|
732011 |
| Filed:
|
July 18, 1991 |
| Current U.S. Class: |
210/640; 210/634; 210/650; 210/651 |
| Intern'l Class: |
B01D 061/36 |
| Field of Search: |
210/651,652,708,799,804,806,640,655,634
427/341,340,342
|
References Cited
U.S. Patent Documents
| 3951815 | Apr., 1976 | Wrasedlo | 210/500.
|
| 4277344 | Jul., 1981 | Cadotte | 210/654.
|
| 4311583 | Jan., 1982 | Woodle | 208/312.
|
| 4328092 | May., 1982 | Sequeira, Jr. | 208/326.
|
| 4464494 | Aug., 1984 | King et al. | 523/400.
|
| 4510047 | Apr., 1985 | Thompson | 210/655.
|
| 4582726 | Apr., 1986 | Shuey et al. | 427/208.
|
| 4592832 | Jun., 1986 | Bristow et al. | 208/309.
|
| 4816140 | Mar., 1989 | Trambouze et al. | 208/309.
|
| 4943475 | Jul., 1990 | Baker et al. | 427/341.
|
| 4978454 | Dec., 1990 | Sweet | 210/644.
|
| Foreign Patent Documents |
| 145126 | Jun., 1985 | EP.
| |
| 217534 | Apr., 1987 | EP.
| |
| 244277 | Nov., 1987 | EP.
| |
| 421676 | Apr., 1991 | EP.
| |
| 2595370 | Sep., 1987 | FR.
| |
| 2595371 | Sep., 1987 | FR.
| |
Other References
"In Situ-Formed Condensation Polymers for Reverse Osmosis Membranes: Second
Phase", North Star Research Institute, Dept. of Interior, NTIS Pub.
#PB234198.
"Continued Evaluation of In Situ-Formed Condensation Polymers for Reverse
Osmosis Membranes", Midwest Research Inst. Dept of Comm. NTIS Pub. #PB
253193.
"Liquid Extraction", 2nd Ed., R. E. Treybol, McGraw-Hill Book Co., 1963,
pp. 144-145; 270-273.
|
Primary Examiner: Spear; Frank
Attorney, Agent or Firm: Allocca; Joseph J.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of U.S. Ser. No. 609,564 filed
Nov. 5, 1990, now abandoned.
Claims
What is claimed is:
1. A method for the selective solvent extraction of aromatic hydrocarbons
from mixtures of same with non-aromatic hydrocarbons in a hydrocarbon feed
stream comprising contacting said hydrocarbon feed stream with a selective
aromatics extraction solvent in a solvent extraction zone to produce an
aromatics rich extract phase and an aromatics lean raffinate phase passing
a side stream comprising a mixed raffinate solution/extract solution which
is taken from an intermediate zone of the solvent extraction zone and fed
to a membrane separation unit whereby said mixed feed is separated into a
solvent-raffinate rich permeate and an extract rich retentate and passing
the extract rich retentate to a settling zone where it spontaneously
separates into an oil rich pseudo raffinate upper phase which is recovered
and into a solvent rich pseudo extract bottoms phase which is recycled to
the solvent extraction zone at a point below that at which the side stream
was withdrawn.
2. A method for the selective solvent extraction of aromatic hydrocarbons
from mixtures of same with non-aromatic hydrocarbons in a hydrocarbon feed
stream comprising contacting said hydrocarbon feed stream with a selective
aromatics extraction solvent in a solvent extraction zone to produce an
aromatics rich extract phase and an aromatics lean raffinate phase,
passing a side stream comprising a mixed raffinate solution/extract
solution which is taken from an intermediate zone of the solvent
extraction zone and fed to a membrane separation unit whereby said mixed
feed is separated into a solvent-raffinate rich permeate and an extract
rich retentate and passing the extract rich retentate to a settling zone
where it spontaneously separates into a oil rich pseudo raffinate upper
phase which is recovered and into a solvent rich pseudo extract bottoms
phase which is recycled to the solvent extraction zone at a point below
that at which the side stream was withdrawn, passing the extract phase
from the solvent extraction zone to a membrane separation unit and
recovering a retentate, passing the retentate to a settling zone wherein
the retentate spontaneously separates into two liquid phases, passing the
upper phase back to the solvent extraction zone to thereby increase the
yield of raffinate and wherein the aromatics rich extract phase contains
from about 5 to 25% oil.
3. The method of claim 1 or 2 wherein the membrane separation zone
comprises an interfacially polymerized crosslinked membrane on microporous
organic solvent resistant ultrafiltration backing, said interfacially
polymerized membrane comprising the reaction product of a multi-functional
amino compound dissolved in water with a polyfunctional agent dissolved in
an organic solvent, at least one of which reactants is trifunctional, on a
backing, and said contacting is under reverse osmosis conditions.
4. The method of claim 3 wherein the multi-functional amino group reactant
is selected from polyethylenimine, polyvinylamine, polyvinylaniline,
polybenylamine, polyvinylimidazolines, amine modified polyepihalohydrines,
m-phenylenediamine, p-phenylenediamine, triaminobenzine, piperazine,
piperidine, 2,4-biz (2-amino-benzyl) aniline, cyclohexane diamine,
cycloheptane diamine.
5. The method of claim 4 wherein the polyfunctional agent is selected from
di- and tri- acid halides, acid anhydrides, aliphatic diisocyanates,
aromatic diisocyanates, thioisocyanates, haloformates, sulfonylhalides and
mixtures thereof.
6. The method of claim 3 wherein the multi-functional amine compound in
water is at a concentration of 0.1 to 10 wt %, and the polyfunctional
agent reactant in organic solvent is at a concentration of 0.1 to 5 wt %.
7. The method of claim 3 wherein the backing is selected from nylon,
cellulose, polyester, teflon, polypropylene, polyethylene,
polyethyleneterephthalate ultrafiltration membranes.
8. The method of claim 3 wherein the ultra-filtration membrane support
layer has pores in the range 0.02 to 0.1 .mu.m.
9. The method of claim 2 wherein the aromatics oil extract phase contains
from about 10 to about 18% oil.
10. The method of claim 2 wherein the permeate from the membrane separation
unit which separates the extract phase from the solvent extraction zone
into a retentate and a permeate is combined with the solvent rich pseudo
extract bottoms phase from the settling zone which uses as feed the
retentate from the membrane separation zone which separates the side
stream taken from the intermediate zone of the solvent extraction zone.
Description
BRIEF DESCRIPTION OF THE INVENTION
The solvent extraction of aromatics containing oil using a selective
aromatics extraction solvent to produce an aromatics rich extract phase
and an oil rich/aromatics lean raffinate is improved by the steps of
subjecting the extract phase preferably containing from about 5 to about
25% oil, more preferably containing about 10 to about 18% oil to a
membrane separation step to produce a permeate phase and a retentate phase
and passing the retentate phase to a settling zone such as a settling drum
wherein the retentate phase spontaneously separates into two liquid
phases. The upper phase, containing good quality lubricating oil molecules
can be recycled to the extraction zone, either to the feed inlet or to the
bottom of the extract reflux zone to thereby increase the raffinate oil
recovered from the extraction tower.
Alternatively or in addition to the above a side stream can be taken from
an intermediate zone of the extraction zone (e.g. extraction tower) and
fed to a membrane separation unit wherein the mixed extract
solution/raffinate solution feed stream taken from the intermediate zone
of the extraction zone is fed to a membrane separation zone to produce a
solvent rich permeate and an oil rich retentate. The solvent rich permeate
is recycled while the oil rich retentate is fed to a settling zone wherein
the oil rich retentate will spontaneously separate into an oil rich pseudo
raffinate upper phase which is recovered and into a solvent rich pseudo
extract bottoms phase which is recycled to the solvent extraction zone,
preferably at a point below that at which the side stream was withdrawn.
The membrane separation zone for the separation of solvent from the extract
phase, raffinate phase or intermediate phase may employ regenerated
cellulose membrane under reverse osmosis conditions as taught in U.S. Pat.
No. 4,510,047 or, preferably the interfacially polymerized membranes
disclosed and claimed in copending application U.S. Ser. No. 417,333 filed
Oct. 5, 1989 in the name of Laura E. Black.
The preferred interfacially polymerized, crosslinked membranes on
microporous, organic solvent resistant ultrafiltration membrane backing
useful for the separation of organic solvents and organic solutes under
reverse osmosis conditions are prepared by depositing an aqueous (or
conversely non-aqueous) solution of a first reactant component on the
microporous backing support layer, draining off the excess quantity of
this first solution and then applying a second reactant component in the
form of a non-aqueous (or conversely aqueous) solution. The two components
interact and polymerize at the interface between the aqueous phase and the
non-aqueous phase to produce a highly crosslinked thin polymer layer on
the micro porous ultrafiltration support backing layer.
The membranes are generally prepared by reacting multi-functional amino
compounds dissolved in water with a second polyfunctional agent dissolved
in organic solvents. The amino compounds can be aliphatic, alicyclic or
aromatic. The polyfunctional agents that the amines are reacted with can
include di- and tri- acid chlorides, acid anhydrides, aliphatic and
aromatic diisocyanates, thioisocyanates, chloroformates and sulfonyl
chlorides. Organic solvent resistant backings which can be used include
nylon (e.g. nylon 66), cellulose, polyester, teflon, polypropylene and
other insoluble polymers. These membranes are useful for separating
mixtures of organic liquids under reverse osmosis conditions. They are
particularly useful for separating aromatics extraction solvents (such as
N-methyl pyrollidone, furfural, phenol etc.) from mixtures of same with
oil or aromatic hydrocarbons in raffinate or extract solutions resulting
from the solvent extract process.
BACKGROUND OF THE INVENTION
The separation of solutes from organic solvents is desirable in many
processes. It would be useful to have a reverse osmosis membrane that was
insoluble in all organic solvents, and showed a high rejection for various
solutes. Such a membrane could be useful in purifying streams that would
degrade or dissolve many other membranes.
Interfacially polymerized membranes were initially discovered in the 1970's
for use in water desalination (see "In Situ-formed Condensation Polymers
for Reverse Osmosis Membranes: Second Phase", North Star Research
Institute, prepared for Department of the Interior, July 1974, available
from NTIS, report #PB-234 198; "Continued Evaluation of In Situ-formed
Condensation Polymers for Reverse Osmosis Membranes", Midwest Research
Institute, prepared for Office of Water Research and Technology, April
1976, available from NTIS, report #PB-253 193; "Interfacially Synthesized
Reverse Osmosis Membrane", U.S. Pat. No. 4,277,344, Jul. 7, 1981, assn. to
Film Tec Corporation). Prior art only describes the use of these membranes
for the separation of aqueous solutions by reverse osmosis. There is no
mention of the use of these membranes for the separation of solutes from
organic solvents by reverse osmosis.
Interfacially polymerized membranes are composed of a highly crosslinked
and generally insoluble condensation polymer which is formed in situ on a
micro-porous film. Most of these membranes are formed with di- or
polyamines which are reacted with multi-functional iso-cyanates or acid
chlorides. Amines react very readily with both of these reactants. Several
of these membranes have been commercialized for water desalination
purposes by companies such as UOP, Film Tec and Desalination Systems Inc.
All of the commercial membranes use a polysulfone ultrafiltration membrane
(0.02 to 0.1 micron pore size) for the microporous support film. Prior art
does describe the use of some other microporous support films such as
polyvinylchloride ultrafiltration membranes but none of the support films
mentioned are particularly resistant to organic solvents.
These membranes are formed using the following procedures. A thin layer of
a dilute solution of one component, usually an aqueous solution of the
amine, is put on one side of the microporous support film. A thin layer of
a dilute solution of the second component, usually in a water immiscible
solvent, is then put on top of the water solution layer. The order of
applying the solutions can be reversed. The two components react at the
water/solvent interface forming a thin (less than 1 micron thick) highly
crosslinked polymer layer. This polymer layer is the active layer of the
membrane at which separation occurs. Some examples of formulations
mentioned in the prior art are reacting polyethylenimine with toluene
diisocyanate, reacting polyethylenimine with isophthaloyl dichloride and
reacting m-phenylene diamine with trimesoyl chloride.
These membranes exhibit high salt rejections from water (>95%). The
commercially available membranes prepared on polysulfone ultrafiltration
membranes are not suitable for separating solutes from organic solvents as
these typically soften or dissolve polysulfone.
French Patent 2,595,370 teaches a multiple effect extraction process using
counter current solvent flow. The process utilizes a main column separated
into 2 zones by a draw off tray and a second column which fractionates the
side stream drawn off from the first column. The fractionation zone
produces an over head raffinate which is fed back to the top zone of
column 1 above the draw-off tray. The bottoms from the fractionation zone
are cooled and separate into a pseudo raffinate and an extract. This
extract is recycled to the bottom zone of column 1 just below the draw-off
tray. It can optionally also be fed into the top zone of column 1 just
above the draw-off tray. By this scheme a raffinate is recovered from the
top of the first column, an extract from the bottom of said column and a
pseudo raffinate from the separation zone to which the bottoms fraction
from the fractionation zone is fed.
In an alternate embodiment the extract from the bottom of column 1 can be
cooled to salt-out in a separation zone an upper phase of lighter
hydrocarbons which is recycled back to the bottom of the bottom zone of
column 1. The bottoms fraction from this separation zone is a true extract
phase.
French Patent 2,595,371 teaches a process for the selective solvent
extraction of a hydrocarbon mixture. Solvent is passed counter currently
to the hydrocarbon feed employing 2 or more separation columns resulting
in the separation of the feed into a raffinate, a pseudo-raffinate and an
extract. Feed is introduced into a first column while fresh solvent is
introduced into the top of a second column. The overheads from the first
column constitute the feed to the second column. The bottoms from the
second column are cooled and permitted to salt-out in a separation zone
wherein an upper phase pseudo raffinate is recovered and a bottom phase of
recycle solvent is recovered. This bottom phase recycle solvent is used as
the solvent introduced into the first column. Extract is recovered from
the bottom of the first column and raffinate from the top of the second
column. In an alternative embodiment part of the pseudo raffinate can be
cycled back to the bottom of the second column while the extract from the
first column can be cooled to salt-out in a separation zone producing a
upper phase of lighter hydrocarbon which is recycled to the bottom of the
first column, and a true extract bottoms phase.
U.S. Pat. No. 4,311,583 teaches a solvent extraction process. A hydrocarbon
feed is contacted with N-methyl pyrollidone in an extraction zone. The
primary extract is separated into a secondary raffinate and a secondary
extract by cooling the primary extract optionally with the addition of
water or wet solvent. The secondary raffinate is separated from the
secondary extract. At least part of the secondary raffinate is combined
with the primary raffinate to obtain an increased yield of desired quality
raffinate oil product. A part of the secondary raffinate may be returned
to the lower part of the extraction zone.
U.S. Pat. No. 4,328,092 teaches the solvent extraction of hydrocarbon oils.
The process uses N-methyl-2-pyrollidone. The extract from the solvent
extraction zone is cooled to form two immiscible liquid phases, a
secondary extract phase and a secondary raffinate phase. The secondary
raffinate phase is recycled to the extraction zone resulting in increased
yield of refined oil product and in energy savings.
"Liquid Extraction" 2d Ed, R. E. Treybol, McGraw-Hill Book Company, 1963
pgs 144-145, 270-273. This reference shows that extractor reflux has been
practiced and that reflux for extraction operations is obtained by
distillation methods, chilling or by the addition of an anti solvent.
DESCRIPTION OF THE FIGURES
FIG. 1 presents a schematic of the present invention practiced on the
extract phase with recycle of the upper phase from the settling zone to
the extraction zone.
FIG. 2 presents a schematic of the present invention practiced on both an
intermediate zone side stream and on the extract phase.
THE PRESENT INVENTION
The solvent extraction of aromatics containing oil using a selective
aromatics extraction solvent to produce an aromatics rich extract phase
and an oil rich/aromatics lean raffinate is improved by the steps of
subjecting the extract phase preferably containing from about 5 to about
25% oil, more preferably containing from about 10 to about 18% oil to a
membrane separation step to produce a permeate phase and a retentate phase
and passing the retentate phase to a settling zone such as a settling drum
wherein the retentate phase spontaneously separates into two liquid
phases. The upper phase, containing good quality lubricating oil molecules
can be recycled to the extraction zone, either to the feed inlet or to the
bottom of the extract reflux zone to thereby increase the raffinate oil
recovered from the extraction tower.
Alternatively or in addition to the above a side stream can be taken from
an intermediate zone of the extraction zone (e.g. extraction tower) and
fed to a membrane separation unit wherein the mixed extract
solution/raffinate solution feed stream taken from the intermediate zone
of the extraction zone is fed to a membrane separation zone to produce a
solvent rich permeate and an oil rich retentate. The solvent rich permeate
is recycled while the oil rich retentate is fed to a settling zone wherein
the oil rich retentate will spontaneously separate into an oil rich pseudo
raffinate upper phase which is recovered and into a solvent rich pseudo
extract bottoms phase which is recycled to the solvent extraction zone,
preferably at a point below that at which the side stream was withdrawn.
Treating a raffinate or a sidestream withdrawn from a separation tower to
separate it into a pseudo raffinate and a pseudo extract by means of
distillation followed by settling or by anti solvent addition and/or
cooling followed by settling have been described on the literature as
recited above. All of these techniques, as well as the present invention
rely on introducing a change in conditions on the solution being treated
so that the solution will spontaneously separate into a pseudo raffinate
and a pseudo extract. However, the conventional methods of distillation,
cooling or anti-solvent addition have drawbacks such that they are not
actually practical to use. For example, cooling of extract solution will
generate only little raffinate, limiting the yield of product to less than
20% on feed. In addition, the pseudo extract solution has to be reheated
substantially before recycling to the tower.
Water addition can produce adequate yield of product, but has to be removed
from the pseudo extract solution before it can be reused, and is therefore
impractical. In addition, addition of water results in a loss of
selectivity.
Distillation could remove part of the solvent, similar to the membrane
unit, but requires a substantial amount of equipment, plus a large
temperature increase to reach the solvent boiling point, followed by an
equally large temperature decrease before the settling drum. Consequently
partial solvent recovery using distillation has always proven to be
impractical.
The process of the present invention overcomes theses disadvantages.
Furthermore, use of membrane separation on the sidestream has additional
benefits compared even to membrane solvent recovery on the extract. Feed
contamination, e.g. Iron sulfide or other particulate matter is less
likely to reach the membrane, and fouling should be less of a problem, and
the extract oil at the sidestream location is less aromatic than the
conventional extract, consequently, less oil will permeate, and any oil
that may permeate has less effect on solvent quality and on it's
subsequent use at the tower top.
The membrane separation zone for the separation of solvent from the extract
phase, raffinate phase or intermediate phase may employ regenerated
cellulose membrane under reverse osmosis conditions as taught in U.S. Pat.
No. 4,510,047 or, preferably the interfacially polymerized membranes
disclosed and claimed in copending application U.S. Ser. No. 417,333 filed
Oct. 5, 1989 in the name of Laura E. Black.
The present invention preferably uses interfacially polymerized membranes
on a solvent resistant backing, for the separation of the aromatic
extraction solvents such as N-methyl pyrollidone (NMP), phenol, sulfolane,
furfural, N,N-dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), and
dimethyl-acetamide (DMAc), preferably NMP, phenol or furfural from oil.
The solvent resistant backing is an ultrafiltration membrane with pore
sizes in the range of 0.02 to 0.1 microns and is composed of generally
insoluble polymers such as nylon 6,6, cellulose, polyester, teflon,
polypropylene and other insoluble polymers, preferably nylon 6,6. It has
been discovered that these membranes provide much higher fluxes and oil
rejections in the separation of extraction solvents from oil than do
commercially available regenerated cellulose membranes (see U.S. Pat. No.
4,510,047).
In the present invention the interfacially polymerized membranes are
prepared by reacting multi-functional amino reactants dissolved in water
with other polyfunctional agent reactants dissolved in organic solvents.
The interfacially polymerized membrane is produced on a non-selective,
microporous ultrafiltration support layer which is inert in the organic
media to which it will be exposed. This support layer is selected from
nylon, cellulose, polyester, teflon, polypropylene, polyethylene
terephthalate etc. ultrafiltration membranes having pores in the range
0.02 .mu. to 0.1 .mu..
A few examples of multi-functional amino group reactants include
polyethylenimine, polyvinylamine, polyvinylanilines, polybenzylamines,
polyvinylimidazolines, amine modified polyepihalohydrins, and other amine
containing polymers, m-phenylene diamine, p-phenylene diamine,
triaminobenzene, piperazine, piperidine, 2,4-bis (p-aminobenzyl) aniline,
cyclohexane diamine, cycloheptane diamine, etc. and mixtures thereof.
The polyfunctional agents that the amines are reacted with can include di-
and tri- acid halides, e.g. chlorides, acid anhydrides, aliphatic and
aromatic diisocyanates, thioisocyanates, haloformates (e.g.
chloroformates) and sulfonyl halides, (e.g. sulfonyl chlorides), and
mixtures thereof. A few examples of these agents are trimesoyl chloride,
cyclohexane-1,3,5 tricarbonyl chloride, isophthaloyl chloride,
terephthaloyl chloride, diisocyanatohexane, cyanuric chloride,
diphenylether disulfonyl chloride, formyl chloride, acetyl chloride,
propionyl chloride, butyryl chloride, valeryl chloride, caproyl chloride,
heptanoyl chloride, valeryl chloride, caproyl chloride, heptanoyl
chloride, octanoyl chloride, pelargonyl chloride, capryl chloride, lauryl
chloride, myristyl chloride, polmityl chloride, margaryl chloride, stearyl
chloride etc., oxalyl chloride, malonyl chloride, succinyl chloride,
glutaryl chloride, fumaryl chloride, glutaconyl chloride, acetic
anhydride, propionic anhydride, butyric anhydride, phthalic anhydride,
ethylene diisocyanate, propylene diisocyanate, benzene diisocyanate,
toluene diisocyanate, naphthalene diisocyanate, methylene bis
(4-phenylisocyanate), ethylene thioisocyanate, toluene thioisocyanate,
naphthalene thioisocyanate, ethylene bischloroformate, propylene
bischloroformate, butylene bischloroformate, 1,3-benzenedisulfonyl
chloride, 1,4 benzene disulfonyl chloride, 1,3-naphthalene disulfonyl
chloride and 1,4-naphthalenedisulfonyl chloride, etc. and mixtures
thereof.
A crosslinked membrane is used in the present invention to ensure stability
in the organic solutions. A crosslinked polymeric film is formed if these
membranes are prepared with one of the reagents being at least
trifunctional. The degree of crosslinking is primarily controlled by the
concentration of the reactant solution with higher concentrations leading
to higher degrees of crosslinking. Membranes prepared from high
concentration solutions generally show higher solute rejections when
tested under reverse osmosis conditions.
In general the interfacially polymerized membranes are produced using 0.1
to 10 wt % aqueous solutions of the amines, preferably 0.25 to 5 wt %
aqueous solutions of the amines; and 0.1 to 5 wt % non-aqueous solutions
of the poly-functional agents, preferably 0.15 to 0.5 wt % non-aqueous
solution of the poly-functional agent.
Following the sequential deposition of the two solutions, the resulting
film can be heated to promote crosslinking of any unreacted amine. This
post heating step can be at a temperature of about 60.degree. to
150.degree. C., preferably 80.degree. to 120.degree. C. for from 1 to 20
minutes. The concentrations of components used and drying/cross-linking
times and temperatures selected from the above ranges will be selected by
the practition in response to the membrane casting procedures actually
employed and the casting machines or other mechanisms or equipment used.
The selective aromatics extraction solvents such as N-methyl-2-pyrollidone
(NMP), phenol, furfural, N,N-dimethylformamide (DMF), dimethylsulfoxide
(DMSO) and dimethylacetamide (DMAC) used to extract aromatic hydrocarbons
from hydrocarbon oils such as specialty oils or white oils are themselves
recovered from the raffinate phase, extract phase or both resulting from
such extraction by permeation under reverse osmosis conditions through the
interfacially polymerized membranes. Reverse osmosis conditions include
contacting the then, interfacially polymerized crosslinked face of the
membrane with the raffinate phase, extract phase, or both, preferably
extract phase at a temperature between about -24.degree. to 200.degree.
C., preferably 40.degree. to 150.degree. C. and under an applied pressure
sufficient to overcome the osmotic pressure. Pressures on the order of 0
to 1000 psig can be used, preferably about 400 to 600 psig.
The aromatic extraction solvent recovered as permeate is recycled to the
beginning of the extraction process or introduced into the extraction zone
somewhat downstream of the fresh solvent inlet at a point where the
composition of the membrane recovered solvent matches the composition of
the solvent/oil mixture in the extraction zone.
In the case of the extraction of lubricating oil stocks, the retentate
recovered from the membrane separation of the extract phase from the
extraction tower is a concentrated extract solution which will
spontaneously separate into two liquid phases when the retentate is
allowed to settle in for example, a settling zone such as a settling drum.
The upper phase from the settling drum will contain good quality
lubricating oil molecules which can be recycled to the extraction tower,
either to the feed inlet or to the bottom of the extract reflux zone in
the extraction tower. This will increase the yield of raffinate oil
recovered from the extraction tower. The bottom phase recovered from the
settling drum can be further treated with membranes for additional solvent
recovery or can be sent to conventional solvent recovery equipment with
the recovered extract being sent on for conventional processing.
Alternatively or in addition to the above, a side stream can be taken from
an intermediate zone of the extraction tower and fed to a membrane
separation unit wherein the mixed raffinate solution/extract solution feed
is separated into a raffinate rich permeate and an extract rich retentate
according to the procedure of U.S. Ser. No. 434,735 filed November 1989 in
the name of James R. Sweet, now U.S. Pat. No. 4,978,454.
According to the present invention the retentate oil rich phase if sent to
a settling zone such as a settling drum will spontaneously separate into
an oil rich pseudo raffinate upper phase which is recovered and into a
solvent rich pseudo extract bottoms phase which is recycled to the solvent
extraction tower preferably at a point below that at which the side stream
was withdrawn.
The separation process could employ the interfacially polymerized membrane
in the form of a spiral wound element. Fabrication of a spiral wound
element would employ adhesives as disclosed in U.S. Pat. Nos. 4,464,494
and 4,582,726, hereby incorporated by reference.
Referring to the figures it is seen in FIG. 1 that hydrocarbon oil feed is
fed via line 1 to the extraction zone (E). Solvent is fed via line 4 into
extraction zone E and passed countercurrently to the hydrocarbon oil feed.
An aromatics lean/oil rich raffinate stream is recovered via line 2 and
sent to the raffinate stripper (not shown) for further processing. An
aromatics rich extract phase is recovered via line 3 and fed to a membrane
separation zone (6) wherein a solvent rich permeate is recovered and
recycled via line 5 to line (4) for re-introduction to the extraction zone
E. A retentate phase is recovered via line 7 and passed to settling zone
(8) wherein it spontaneously separates into two liquid phases. The upper
phase containing good quality lube oil molecules is recycled via line 9
back to extraction zone E and fed into extraction zone E via either line
10 at the bottom of the zone or via line 11 back to the feed inlet line 1.
The bottoms layer from settler 8 may be fed via line 13 to membrane
separation unit 14 wherein a solvent rich permeate is recovered via line
16 and recycled to line 4 for re-introduction to extraction zone E. The
retentate is recovered via line 15 and sent to the extract stripper, not
shown, for further processing. Alternatively, the bottoms phase from
settler 8 may be sent via bypass line (17) directly to the extract
stripper (not shown) for further processing.
FIG. 2 is a variant of the current process. Hydrocarbon feed is introduced
via line (1) into extraction zone (2). Fresh and/or recycled solvent is
fed into extraction zone (2) via line (3). The solvent and hydrocarbon
feed are countercurrently contacted in zone (2). An intermediate
extraction solution stream is withdrawn from zone (2) via line (6) and fed
to membrane separation zone (Ml) wherein a solvent rich permeate stream is
recovered via line (7) and recycled to zone (2) via line (3). A retentate
phase is recovered via line (8) and fed to a settling zone (9) wherein it
spontaneously separates into two liquid phases, a pseudo raffinate
recovered via line (10) and a pseudo extract recovered via line (11) and
fed via line (12) back to the extraction zone (2) at a point somewhat
lower than that at which the intermediate zone side stream was withdrawn.
An extract phase is recovered from zone (2) via line (5) and fed to
membrane separation zone (M2) wherein a solvent rich permeate is recovered
via line (13) and recycled to lines (11) and (12) for re-introduction into
the extraction zone (2). A retentate is recovered via line (14) and fed to
a settling zone 15 wherein the retentate spontaneously separates into two
liquid phases. The upper phase containing good quality oil molecules is
recycled via line 16 to line 1 for introduction as feed back into
extraction zone 2. The bottoms phase recovered via line 17 can be
separated into solvent and extract in a membrane zone or other separation
zone (not shown) for appropriate disposition.
EXPERIMENTAL
Example 1
A 50 wt % water solution of polyethylenimine was used as supplied from
Aldrich (Aldrich cat #18,197-8). A sample of diphenyl methane -4,4
diisocyanate (also referred to as methylene diisocyanate or MDI) was used
as received from BASF Wyandotte Corporation. Ultipor nylon 66 membranes
with 0.1 .mu. pore size were used as supplied by Pall Ultrafine Filtration
Corporation.
The polyethylenimine (PEI) was further diluted with deionized water to
prepare several solutions with various PEI concentrations ranging from
0.35 to 2.6 wt %. A toluene/hexane solution containing approximately 0.4
wt % MDI was prepared. Several membranes were prepared using the following
procedure.
A disc of the nylon 6,6 membrane support was installed in a wash coat cell
where one side of the membrane was left exposed. A polyethylenimine
solution was poured over the exposed side of the membrane and was allowed
to remain for 1 minute. The excess solution was then drained off the
membrane for 1 minute. The MDI solution was then poured over the exposed
side of the membrane and was allowed to remain for 1 minute and was then
drained for 1 minute. The membrane was then placed in an oven (at
temperatures >100.degree. C.) for 10 minutes. After this heat treatment,
the resulting interfacially polymerized, crosslinked polyurea membrane was
ready for testing.
The membrane performance was tested by circulating a sample of an extract
oil solution (average molecule weight of oil=400 g/mole) containing 12 vol
% oil in NMP over the thin interfacially polymerized crosslinked face of
the membranes at 70.degree. C. and at an applied feed pressure of 500
PSIG. The permeate yield was kept below 5% to ensure that the feed
composition did not change during testing. The membranes were tested for 2
to 3 hours, during which time the membrane flux was recorded and permeate
samples collected. The membranes were then left in the test unit overnight
in the extract solution at ambient temperatures with no applied feed
pressure. The next morning, the membranes were retested for an additional
2 to 3 hours with additional permeate samples being collected. The volume
percent oil in both the feed and the permeate samples were measured.
The interfacially polymerized membranes had fluxes ranging from about 200
to 750 1/m.sup.2 day with corresponding oil rejections of >98 vol % to 88
vol % (Table 1). Both the concentration of the polyethylenimine in the
water wash solution and the heat treatment temperature affected the
membrane performance. The high oil rejection of >98% was obtained with the
highest PEI concentration tested of 2.63%.
TABLE 1
______________________________________
EQUILIBRIUM PERFORMANCE OF INTERFACIALLY
POLYMERIZED MEMBRANES*
Temperature =
70.degree. C.
Pressure = 500 psig
Feed = 12 vol % 150N extract oil/NMP
Membrane : prepared by reacting aqueous solution of
polyethylenimine with 0.4 wt % methylene
diisocyanate in toluene/hexane on a 0.1.mu.
nylon 6,6 ultrafiltration membrane
Oil Re-
Run wt % PEI Heat Treatment
Flux jection (1)
No. in Water Temperature .degree.C.
l/m.sup.2 day
vol %
______________________________________
A 2.63 135 210 >98
B 2.63 145 196 >98
C 0.67 145 750 88
D 0.67 112 330 94
E 0.35 112 477 96
______________________________________
*performance at end of the second test period after the membranes had
soaked in the feed solution overnight
(1) oil rejection accurate to .+-.1.5 vol %
After the overnight soak period, the flux exhibited by the membranes
increased by about 50 1/m.sup.2 day. The reason for this increase is not
understood. The membrane rejection stayed essentially the same or
increased in a couple of cases. The long term stability of these membranes
in NMP solutions is not yet known.
Example 2
A 50 wt % aqueous solution of polyethylenimine was used as supplied from
Aldrich (Aldrich cat #18,197-8). Samples of diphenyl methane -4,4
diisocyanate (also referred to as methylene diisocyanate or MDI) and
toluene diisocyanate were used as received from BASF. Isophthaloyl
dichloride (IPDC), trimesoyl chloride, 1,3-phenylene diamine and
1,4-phenylene diamine (1,4-PDA) were used as supplied from Aldrich.
Ultipor nylon 6,6 membranes with 0.04 .mu. pore size were used as support
membranes as supplied by Pall Ultrafine Filtration Corporation.
Membranes prepared by reacting polyethylenimine with methylene diisocyanate
were made as follows. The PEI was diluted with deionized water to prepare
several solutions with PEI concentrations ranging from 0.25 to 1.0 wt %.
The MDI was dissolved in a 35/15 w/w toluene/hexane mixture to prepare
several solutions with MDI concentrations ranging from 0.25 to 0.6 wt %. A
disc of the nylon 6,6 membrane was installed in a wash coat cell where one
side of the membrane was left exposed. A polyethylenimine solution was
poured over the exposed side of the membrane and was allowed to remain for
one minute. The excess solution was then drained off the membrane for one
minute The MDI solution was then poured over the same exposed side of the
membrane and was allowed to remain for one minute and was then also
drained for one minute. The membrane was then placed in an oven at
110.degree. C. for 10 minutes. After this heat treatment, the membrane was
ready for testing.
Membranes prepared by reacting polyethylenimine with toluene diisocyanate
were made in the same manner as described above, except that TDI solutions
in hexane with concentrations ranging from 0.25% to 0.5% were used.
Similarly, membranes prepared by reacting polyethylenimine with
isophthaloyl dichloride were made in the same manner except that IPDC
solutions in hexane with concentrations ranging from 0.5% to 1.0% were
used. Membranes prepared by reacting 1,4 phenylene diamine with trimesoyl
chloride were made in the same manner using aqueous solutions of 1,4-PDA
ranging in concentration from 1 to 4% and hexane solutions of TMC ranging
in concentration from 0.15 to 0.5%. The PDA/TMC membranes were not heat
treated. Similarly, interfacially polymerized, crosslinked polyamide
membranes prepared by reacting 1,3-phenylene diamine with trimesoyl
chloride were made in the same manner except that aqueous solutions of
1,3-PDA ranging in concentration from 1 to 4% were used.
Membrane performance was determined by circulating a sample of an extract
oil solution (average molecular weight of oil=400 g/mole) containing 13
vol % oil in NMP over the membranes at 70 C at an applied feed pressure of
500 PSIG. The permeate yield was kept below 5% to ensure that the feed
composition did not change during testing. The membrane flux was recorded
and permeate samples collected. The volume percent oil in both the feed
and permeate samples was measured.
The Polyethylenimine Based Membranes
For interfacial membranes prepared from polyethylenimine and methylene
diisocyanate, fluxes ranging from 94 to 500 l/m.sup.2 day and oil
rejections ranging from 90 to 99 vol % (accurate to 1.5 vol %) were
obtained (Table 2). The most important parameter controlling the
performance of these membranes was the concentration of the aqueous PEI
solution. The concentration of the MDI solution (over the ranges studied)
had only a minor effect. As the PEI concentration increased from 0.25 to
1.0 wt %, the oil rejection increased from 92 to 99 vol % and the flux
decreased from 500 to 94 l/m.sup.2 day for membranes made with MDI
concentrations of 0.5%. Increasing the MDI concentration from 0.25 to 0.6
wt % appeared to decrease the oil rejection slightly from 94 to 90% at low
PEI concentrations but did not appear to have any effect at higher PEI
concentrations. This slight decrease might not be a real effect as the
rejection is only accurate to 1.5 vol %.
The effect of the MDI concentration on flux is not as clear. At high PEI
concentrations, the MDI concentrations (within the range studied) appeared
to have little effect. At lower PEI concentrations, the 0.5% MDI membranes
appeared to have higher fluxes than membranes made with either lower or
higher MDI concentrations. The optimum membrane for NMP/oil separations
was prepared from solutions containing 0.25% PEI and 0.5% MDI which gave
an oil rejection of 92 vol % and a flux of 500 l/m.sup.2 day.
Interfacial membranes prepared from polyethylenimine and toluene
diisocyanate showed similar trends. Oil rejections ranging from 90.8 to 99
vol % and fluxes ranging from 10 to 411 l/m.sup.2 day were obtained (Table
3). Again, the PEI concentration was the most important factor controlling
membrane performance. The TDI concentration (over the range studied) did
not have any significant effect. As the PEI concentration increased from
0.25 to 1.0%, the oil rejection increased from approximately 91 to 99 vol
% and the flux declined from 300-400 down to 10-50 l/m.sup.2 day.
In comparing membranes made with MDI and TDI, little difference can be
observed for the oil rejection of membranes prepared using the same
concentrations of reactants. Membranes prepared with MDI seem to show a
slightly lower oil rejection (96 vol % vs 99 vol % at 0.5% PEI) but this
is within the range of accuracy of these values. A major difference can be
observed, however, for the fluxes exhibited by the membranes. Membranes
made with MDI, in comparison to membranes made with TDI, at the same
reactant concentrations, exhibit fluxes twice as high. For example,
membranes prepared from a 0.25% PEI solution and a 0.5% MDI or TDI
solution both gave an oil rejection of 92% but exhibited fluxes of 497 and
280 respectively. MDI is clearly preferred over TDI since it results in
higher flux membranes.
Interfacially polymerized membranes were prepared by reacting
polyethylenimine with isophthaloyl dichloride (Table 4). Surprisingly,
these membranes exhibited low oil rejections of about 78 vol % with fluxes
of 294 l/m.sup.2 day. According to literature (J. Macrmol. Sci.--Chem A15
(5) pp 727-755, 1981) a membrane prepared by reacting 0.5% IPC in hexane
with 0.67% PEI in water, exhibits a high salt rejection from water of
99.3%. From this it can be seen that there is no direct correlation
between membrane salt rejection performance and membrane oil rejection
performance.
Overall, the major factors controlling the flux and oil rejection exhibited
by polyethylenimine based membranes are the identity of the isocyanate or
acid chlorides and the solution concentration of the reactants. Membranes
reacted with MDI show higher fluxes than do membranes reacted with TDI.
The flux and rejection exhibited by a membrane prepared with a particular
isocyanate is controlled primarily by the solution concentration of the
imine, e.g. PEI. While high rejection membranes were not obtained using
isophthaloyl dichloride instead of the isocyanates, the membranes produced
did exhibit the ability to separate mixtures of organic solvents and
solutes under reverse osmosis conditions.
The Phenylene Diamine Based Membranes
The phenylene diamine based membranes are usually reacted with an acid
chloride such as trimesoyl chloride.
For interfacial membranes prepared from 1,4 phenylene diamine and trimesoyl
chloride, oil rejections ranging from 58.5 to 97 vol % and fluxes ranging
from 1270 to 580 l/m.sup.2 day were obtained. (Table 5). For these
membranes, both the concentration of 1,4 phenylene diamine in water and
trimesoyl chloride in hexane were important in controlling their
performance. As the concentration of TMC increased for a given PDA
concentration, the oil rejection decreased and the flux increased. This
effect was particularly noticeable at the lowest PDA concentration tested
at 1%. At 4%, PDA, as the TMC concentration increased from 0.15 to 0.5%,
the rejection decreased from approximately 96 to 90 vol % and the flux
stayed relatively constant at close to 600 l/m.sup.2 day. Higher
concentrations of TMC might be expected to yield more highly crosslinked
and hence higher rejection membranes.
The PDA concentration also had a strong impact on membrane performance. As
expected, as the PDA concentration increased, the oil rejection increased
and the flux decreased. The optimum membrane for NMP/oil separation was
prepared from solutions containing 4% PDA and 0.15% TMC; this gave an oil
rejection of 95 to 97 vol % with fluxes of 580 l/m.sup.2 day. Slightly
lower TMC and/or slightly higher PDA concentration might give a membrane
with somewhat better performance. The optimum membrane shows both higher
fluxes and oil rejections than the optimum PEI/MDI membrane which gave an
oil rejection of 92 vol % at a flux of 500 l/m.sup.2 day. Among the
membranes tested, the 1,4 PDA/TMC membranes appear to be the optimum for
the NMP/oil separation.
Surprisingly, for an interfacially polymerized membrane prepared from a 4%
water solution of 1,3-phenylene diamine and a 0.15% hexane solution of
trimesoyl chloride, an oil rejection of 70 vol % with a flux of 1050
l/m.sup.2 day was exhibited (Table 6). According to literature, (U.S. Pat.
No. 4,277,344) these membranes exhibit salt rejections of over 99% from
aqueous solutions. Again, it can be seen that there is no direct
correlation between membrane salt rejection performance and membrane oil
rejection performance.
The optimum interfacially polymerized membrane was prepared by reacting a
4% water solution of 1,4 phenylene diamine with a 0.15% solution of
trimesoyl chloride in hexane on a nylon 6,6 ultrafiltration membrane. This
membrane gave an oil rejection of approximately 96 vol % at a flux of
approximately 600 l/m.sup.2 day for the separation of NMP from extract
oil at 70.degree. C. and a feed pressure of 500 PSIG. Both the
concentration of the diamine and the acid chloride are important in
controlling the performance of the membrane.
TABLE 2
______________________________________
PERFORMANCE OF POLYETHYLENIMINE/
METHYLENE DIISOCYANATE MEMBRANES
Feed = 13 vol % 150N extract oil/NMP
Temperature=
70.degree. C.
Pressure = 500 PSIG
Membrane = methylene diisocyanate in 35/15 toluene/
hexane reacted with polyethylenimine in
water on a 0.04.mu. nylon membrane
Wt % Wt % Flux Oil Rejection
MDI PEI (l/m.sup.2 day)
(vol. %)
______________________________________
0.25 0.25 221 94.6
0.50 128 96.1
0.67 143 97.6
1.0 103 98.5
0.5 0.25 497 92.3
0.50 223 96.2
0.67 112 --
1.0 94 99.0
0.6 0.25 323 90.0
0.5 (a) 1.0 50 99.0
0.5 (a) 0.25 197 99.0
______________________________________
(a) MDI dissolved in toluene
TABLE 3
______________________________________
PERFORMANCE OF POLYETHYLENIMINE/TOLUENE
DIISOCYANATE MEMBRANES
Feed = 13 vol % 150N extract oil/NMP
Temperature =
70.degree. C.
Pressure = 500 PSIG
Membrane = toluene diisocyanate in hexane
reacted with polyethylenimine in
water on a 0.04.mu. nylon membrane
Wt % Wt % Flux Oil Rejection
TDI PEI (l/m.sup.2 day)
(vol %)
______________________________________
0.25 0.25 411 90.8
0.5 76 98.5
1.0 10 98.0
0.50 0.25 280 92.3
0.50 60 99.0
1.0 45 99.0
______________________________________
TABLE 4
______________________________________
PERFORMANCE OF POLYETHYLENIMINE/
ISOPHTHALOYL DICHLORIDE MEMBRANES
Feed = 13 vol % 150N extract oil/NMP
Temperature =
70.degree. C.
Pressure = 500 PSIG
Membrane = isophthaloyl dichloride in hexane
reacted with polyethylenimine in
water on a 0.04.mu. nylon membrane
Wt % Wt % Flux Oil Rejection
IPC PEI (l/m.sup.2 day)
(vol %)
______________________________________
0.5 0.67 294 78.5
1.0 1.0 123 76.9
______________________________________
TABLE 5
______________________________________
PERFORMANCE OF 1,4-PHENYLENE DIAMINE/
TRIMESOYL CHLORIDE MEMBRANES
Feed = 13 vol % MCT 10 extract oil/NMP
Temperature =
70.degree. C.
Pressure = 500 PSIG
Membrane = trimesoyl chloride in hexane
reacted with 1,4 phenylene diamine in
water on a 0.04.mu. nylon membrane
Wt % Wt % Flux Oil Rejection
1,4-PDA TMC (l/m.sup.2 day)
(vol %)
______________________________________
1.0 0.15 1050 87.7
0.38 1270 58.5
0.50 1470 70.8
2.0 0.50 1100 81.4
4.0 0.15 802 96.9
4.0 0.15 580 95.4
4.0 0.5 615 90.8
______________________________________
1,4-PDA = 1,4 phenylene diamine
TMC = trimesoyl chloride
TABLE 6
______________________________________
PERFORMANCE OF 1,3-PHENYLENE DIAMINE/
TRIMESOYL CHLORIDE MEMBRANES
Feed = 13 vol % extract oil/NMP
Temperature =
70.degree. C.
Pressure = 500 PSIG
Membrane = trimexoyl chloride in hexane reacted
with 1,3-phenylene diamine in water
on a 0.04.mu.nylon membrane
Wt % Wt % Flux Oil Rejection
1,3-PDA TMC (l/m.sup.2 day)
(vol %)
______________________________________
4 0.15 1050 70
______________________________________
Example 3
Membranes were prepared in a continuous manner on an interfacial
polymerization machine using nylon 6,6 membrane with 0.04 .mu. pore size
obtained from Pall Ultrafine Filtration Corporation as support. Solutions
were prepared of 4% 1,4-phenylene diamine in water and 0.14% trimesoyl
chloride in Chevron 250B.
The membranes were prepared in a continuous manner on an interfacial
polymerization machine. The nylon membrane support was moved through the
machine by means of rollers at a web speed of 3 feet per minute. The nylon
membrane first contacted a trough containing the amine solution at
40.degree. C., was then allowed to partially dry as it travelled by
rollers to a second trough where it contacted the trimesoyl chloride
solution at room temperature. The membrane then travelled through an oven
where it was heated at 125.degree. F. for 5 minutes.
The contact time of the nylon membranes with the reactant solutions and the
time of evaporation between contacting the amine solution and the
trimesoyl chloride solution were different from laboratory conditions due
to the physical constraints of the IFP machine. The contact time in the
amine solution was 18 seconds (versus 1 minute in the laboratory). The
evaporation period between the solutions was 3 minutes and 25 seconds
(versus 1 minute in the laboratory). The contact time in the trimesoyl
chloride solution was 12 seconds (versus 1 minute in the laboratory). The
following results were obtained from 4 different runs on the IFP machine.
Membrane performance was determined by circulating a sample of an extract
oil solution (average molecular weight of oil=400 g/mole) containing 14
vol % oil in NMP over the membrane at 70.degree. C. at an applied feed
pressure of 500 PSIG. The permeate yield was kept below 5% to ensure that
the feed composition did not change during testing. The membrane flux was
recorded and permeate samples collected. The volume percent oil in both
the feed and permeate samples was measured.
______________________________________
Flux Oil Rejection
Membrane l/m.sup.2 day
vol %
______________________________________
A 413 90
B 500 93
C 475 90
D 650 71
______________________________________
The membrane flux observed was comparable to the laboratory prepared
membranes but the oil rejection was somewhat erratic and lower than the
laboratory results. These results were attributed to the following. The
nylon 6,6 membrane is very hydrophobic. It does not become completely
saturated with the aqueous amine solution during the 18 seconds of
contact. The aqueous solution then wicks into the interior of the nylon
membrane during the evaporation period. The short contact time with the
trimesoyl chloride solution may not have been sufficient for adequate
contact with the PDA solution in the interior of the membrane leading to
defects in the membrane.
These membranes were also observed to contain crystals of PDA as a result
of using a saturated aqueous solution of PDA. The adhesive used for
element manufacture exhibited very poor bonds with these membranes
containing crystals and hence these membranes were unacceptable.
Example 4
An effort was made to reduce the crystals in the membranes by reducing the
concentration of the amine solution keeping other factors constant. The
following results were obtained on testing these membranes using the same
test conditions as before.
______________________________________
Flux Oil Rejection
Membrane % 1, 4-PDA l/m.sup.2 day
vol %
______________________________________
E 3.5 525 86
F 2.0 400 71
______________________________________
As the 1,4-PDA concentration decreased to 2.0%, the oil rejection decreased
to 71 vol %. In contrast, a laboratory sample made with an even lower
concentration of 1,4 PDA of 1% showed an oil rejection of 87.7%. (See
Table 5). The poor result of the machine produced membranes can be
attributed to the very short contact times in the reactant baths. It is
known in the prior art that longer contact times can increase the extent
of reaction occurring between the two reactants (U.S. Pat. No. 3,951,815).
The contact time between the reactants was increased to approximately that
of the laboratory study.
The web speed on the IFP machine was changed to 1 foot per minute. This
increased the contact time in the amine solution to 50 seconds, the
in-between evaporation period to 10 minutes and 25 seconds, and the
contact time in the trimesoyl chloride solution to 45 seconds. Backside
wetting of the nylon membrane in the amine solution plus the longer
contact time ensured that the nylon membrane was saturated with the amine
solution and that adequate reaction occurred in the trimesoyl chloride
bath. Membranes were prepared with varying amine concentrations and were
reacted with a 0.25% trimesoyl chloride solution. Using the same test
procedure as before, the following results were attained.
______________________________________
Flux Oil Rejection
Membrane % 1, 4-PDA l/m.sup.2 day
vol %
______________________________________
G 2.0 350 96
H 2.0 315 96
I 1.2 340 96
J 0.6 400 92
K 0.3 325 88
______________________________________
Down to an amine concentration of 1.2%, membranes with 96 vol % oil
rejection were obtained. These membranes contained no crystals and
exhibited strong bonds with the adhesive used for element preparation.
Example 5
A vacuum gas oil distillate, having a viscosity of 4.93 cSt at 100.degree.
C., a refractive index of 1.4538 at 75.degree. C., and a density of 0.8668
kg/dm3 at 15.degree. C., was countercurrently contacted in a commercial
extraction tower with NMP containing 2.1% water. The tower bottoms
temperature was 52.degree. C.
A part of the extract solution, containing 9.7 wt. % oil was passed through
a membrane unit, using an interfacially polymerized membrane of
1,4-phenylene diamine and trimesoyl chloride, operating at 93.degree. C.,
which recovered a predominantly NMP permeate. The retentate of this unit,
now containing 12.9 wt. % oil was equilibrated at the tower bottoms
temperature of 52.degree. C. to produce a pseudo raffinate.
In a preferred mode of the invention, the equilibration settling drum and
the membrane unit operate at the extraction tower bottoms temperature,
which can be accomplished by lowering the membrane unit operating
temperature, or by increasing the extraction tower temperature. The
extraction tower temperature can be increased without affecting the
product quality by lowering the solvent treat ratio and/or by increasing
the solvent water content.
Material balance data around the extraction tower, the membrane unit and
the settling drum indicated that 3.2 grams of pseudo raffinate solution
was produced for every 100 grams of feed. Side by side extraction runs of
distillate and a blended bead of distillate and pseudo raffinate in a
countercurrent laboratory extraction unit are illustrated in the following
table.
TABLE 7
______________________________________
Base Base Recycle
Case 1 Case 2 Case
______________________________________
Distillate feed, wt.
100 100 100
Pseudo raffinate,
0 0 3.2
wt % on distillate
Raffinate RI 1.4538 1.4534 1.4536
Raffinate Density
0.8665 0.8658 0.8666
Solvent Treat 186 194 190
(LV % on distillate)
Raffinate Yield
80.8 79.6 83.5
(LV % on distillate)
Adjusted Raffinate Yield.sup.1
80.5 80.4 83.3
(LV % on distillate)
______________________________________
.sup.1 After correction to equal raffinate quality and 186% solvent treat
Results clearly illustrate the superior yield that is obtained by using the
current invention.
Example 6
To determine preferred operating ranges for the invention, three primary
extract solutions were prepared, with different oil concentrations.
Subsequently, the NMP content of the solution was reduced, while the
solution was maintained at the miscibility temperature of the base case,
and the quantity and quality of the pseudo raffinate oil was measured.
Results are shown in the following table.
TABLE 8
______________________________________
Run A: Primary extract with
9.7% oil
NMP Reduction Base -27%
removed by membrane
Oil concentration
9.7 12.9
Pseudo Raffinate Yield,
-- 13.8
LV % on extract oil
Base Case Extract RI
1.5426
Pseudo Raffinate RI @ 75 C
-- 1.4651
Run B: Primary extract with
18% oil
NMP Reduction (simulated)
Base -20% -40% -60%
Oil concentration
18 22 27 35
Pseudo Raffinate Yield,
-- 8.1 12.6 19.3
LV % on extract oil
Base Case Extract RI
1.5287
Pseudo Raffinate RI @ 75 C
-- 1.4678 1.4733
1.4821
Run C: Primary extract with
24% oil
NMP Reduction (simulated)
Base -20% -40%
Oil concentration
24 28 34
Pseudo Raffinate Yield,
-- 0.7 0.8
LV % on extract oil
Base Case Extract RI
1.5287
Pseudo Raffinate RI @ 75 C
-- 1.4813 1.4888
______________________________________
In Run A, NMP removal was accomplished by permeating part of the solution
through a membrane, while in Run B and C, the membrane solvent removal was
simulated by blending of extract oil and solvent in the appropriate
proportions.
The table illustrates that solvent removal generates effectively a pseudo
raffinate if the initial extract oil concentration is 10 and 18% oil, but
is less effective if the initial oil concentration is 24%. It is expected
that the invention will perform well with initial primary extract
concentrations of less than 10% oil, but that the economic attractiveness
of the primary extraction step would decrease because of the large
quantities of solvent that would be required. Thus, the preferred primary
extract oil concentration is between 5 and 25% oil in extract solution,
and the most preferred oil concentration between 10 and 18% oil.
It is interesting to note that in Run B, solvent removal beyond the 24% oil
concentration demonstrated in Run C remains effective in generating more
pseudo raffinate, and that apparently the initial concentration of the oil
is the main factor determining the quantity and quality of pseudo
raffinate. However, at very high oil concentrations, the physical
separation of the pseudo raffinate from the retentate in the settling
vessel becomes more difficult, and the preferred oil concentration in the
retentate of the membrane unit is between 10 and 35%, and most
preferentially between 13 and 25%.
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